U.S. patent application number 13/922563 was filed with the patent office on 2013-10-31 for process for making a stiffened paper.
The applicant listed for this patent is P.H. Glatfelter Company. Invention is credited to Thomas W. Ballinger.
Application Number | 20130284388 13/922563 |
Document ID | / |
Family ID | 49476313 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130284388 |
Kind Code |
A1 |
Ballinger; Thomas W. |
October 31, 2013 |
PROCESS FOR MAKING A STIFFENED PAPER
Abstract
A process for making a stiffened and rigid paper includes
preparing a pulp slurry consisting essentially of water, a
cellulosic pulp, a crosslinker, and a starch, and optionally a
binder; draining the liquid from the pulp slurry to form a web; and
drying the web. Alternatively, a process for making a stiffened and
rigid paper includes the step of adding at least one crosslinker at
one or more locations, such as at the wet-end, dry-end, or at both
ends of the papermaking process. Suitable crosslinkers include a
glyoxal-containing crosslinker, a gluteraldehyde, a polyfunctional
aziridine, a zirconium-containing crosslinker, a
titanium-containing crosslinker, and an epichlorohydrin, and
mixtures thereof. When a binder is employed, it can be added either
in the dry or wet form. Provided is a neutral or alkaline process
to produce a paper product having the improved mechanical
properties of a laminated product in the Z-direction, without a
lamination step.
Inventors: |
Ballinger; Thomas W.;
(Thomasville, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
P.H. Glatfelter Company |
York |
PA |
US |
|
|
Family ID: |
49476313 |
Appl. No.: |
13/922563 |
Filed: |
June 20, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13080217 |
Apr 5, 2011 |
8496784 |
|
|
13922563 |
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Current U.S.
Class: |
162/161 ;
162/162; 162/168.1; 162/174; 162/175; 162/176; 162/178 |
Current CPC
Class: |
D21H 17/36 20130101;
D21H 17/38 20130101; D21H 21/18 20130101; D21H 17/68 20130101 |
Class at
Publication: |
162/161 ;
162/175; 162/174; 162/168.1; 162/178; 162/176; 162/162 |
International
Class: |
D21H 21/18 20060101
D21H021/18 |
Claims
1. A process for making a stiffened and rigid paper, the process
comprising: (i) preparing a pulp slurry consisting essentially of
water, a cellulosic pulp, a starch, optionally a crosslinker,
optionally a papermaking additive, and optionally a binder, wherein
when the binder is included the binder is added to the slurry
separately from the crosslinker; (ii) draining the liquid from the
pulp slurry to form a web; (iii) optionally, adding the crosslinker
to the web; and (iv) drying the web to produce a paper product,
wherein the crosslinker is added either to the web or when
preparing the pulp slurry, or both in an amount effective to
produce the paper product with a basis weight of about 60 lbs/3300
ft 2 to about 400 lbs/3300 ft 2.
2. The process of claim 1, wherein the crosslinker is selected from
the group consisting of a glyoxal-containing crosslinker, a
gluteraldehyde, a polyfunctional aziridine, a zirconium-containing
crosslinker, a titanium-containing crosslinker, and an
epichlorohydrin, and mixtures thereof.
3. The process of claim 1, wherein the crosslinker is a
glyoxal-containing crosslinker.
4. The process of claim 1, wherein the crosslinker is present in
the pulp slurry in an amount of at least about 0.3 weight percent
based on the weight of the solids in the pulp slurry.
5. The process of claim 1, wherein the crosslinker is present in
the pulp slurry in an amount between about 0.3 to about 20 weight
percent based on the weight of the solids in the pulp slurry.
6. The process of claim 1, wherein the crosslinker is present in
the pulp slurry in an amount between about 0.3 to about 10 weight
percent based on the weight of the solids in the pulp slurry.
7. The process of claim 1, wherein the crosslinker is present in
the pulp slurry in an amount between about 1.5 to about 20 weight
percent based on the weight of the solids in the pulp slurry.
8. The process of claim 1, wherein the pulp slurry consists
essentially of the water, the cellulosic pulp, the crosslinker, the
starch, the binder, and optionally the paper making additive.
9. The process of claim 7, wherein the binder is selected from the
group consisting of starch, casein, protein binders, carboxymethyl
cellulose (CMC), polyvinyl alcohol (PVOH), Gum products, and
gelatins, and mixtures thereof.
10. The process of claim 7, wherein the binder is polyvinyl alcohol
(PVOH).
11. The process of claim 1, wherein the pulp slurry includes the
papermaking additive selected from the group consisting of
retention aids, drainage aids, flocculants, dyes, dye fixatives,
inks, colorants, whiteners, brighteners, opacifiers, fillers,
perfumes, microorganism control agents, agents for controlling
non-biological deposits, alum, internal sizing agents, foam control
agents, pH control agents, and mixtures thereof.
12. The process of claim 1, wherein the process does not include
use of a hydrophilic polyacrylamide applied to the web at a size
press.
13. The process of claim 1, wherein the process does not include
use of a hydrophilic polyacrylamide in a mixture with a hydrophobic
surface size agent.
14. The process of claim 1, wherein the paper product has a water
Cobb value greater than 50.
15. The process of claim 1, wherein the paper product has a water
Cobb value greater than 200.
16. The process of claim 1, wherein the at least one crosslinker is
added by spraying the crosslinker onto the web.
17. The process of claim 1, wherein the at least one crosslinker is
added at a size press.
18. The process of claim 1, wherein the at least one crosslinker is
added by spraying the crosslinker onto the web and added at a size
press.
19. The process of claim 1, wherein adding the at least one
crosslinker to the web comprises first forming a crosslinker slurry
and then adding the crosslinker slurry to the web.
20. The process of claim 1, wherein the crosslinker is added in an
amount effective to provide an unlaminated sheet of paper having a
stiffness of within 10% of, and a rigidity at least equal to, an
equal caliper laminated sheet for a basis weight in the range of 60
lbs/3300 ft 2 to 400 lbs/3300 ft 2.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 13/080,217 filed Apr. 5, 2011 the disclosure
of which is incorporated herein by reference in its entirety for
all purposes.
FIELD OF THE INVENTION
[0002] The present invention relates to a method for making a
paper-based product which contains a crosslinker. The present
invention also relates to manufactured paper products which exhibit
increased stiffness and rigidity.
BACKGROUND OF THE INVENTION
[0003] The papermaking industry as well as other industries have
long sought methods for enhancing the strength of products formed
from fibrous materials such as, for example, paper and board
products formed of cellulose fiber or pulp as a constituent. The
dry-strength and related properties of a sheet formed from fibrous
materials are especially important for various purposes. The
problems and limitations presented by inadequate dry-strength have
been particularly acute in the numerous industries where recycled
furnish or fiber mechanically-derived from wood is utilized in
whole or in part. In the papermaking industry for example, recycled
cellulose fiber is typically used in the manufacture of newsprint
and lightweight coated papers. These recycled fibers, however, are
of a generally shorter length than chemically-pulped fibers. Paper
produced from the shorter length recycled fibers have been found to
have relatively poor dry-strength properties in comparison to paper
manufactured from virgin, chemically-pulped fiber. The use of
virgin chemically pulped fiber for all paper and board production,
however, is extremely wasteful in terms of natural resource
utilization and is cost-prohibitive in most instances and
applications.
[0004] Various methods have been suggested in the past for
improving the dry-strength and related properties of a sheet formed
from fibrous materials such as paper or board materials formed of
cellulose fiber. One method known in the art for improving the
dry-strength properties of paper products, for example, involves
the surface sizing of the sheet at a size press after its
formation. While some of the critical properties of the product may
be improved through sizing the surface of the sheets, not all
equipment is amenable for such processes. Many papermaking
machines, for example, including board and newsprint machines, are
not equipped with a size press. Moreover, only the properties of
the surface of the sheet are appreciably improved through surface
sizing. Surface sizing, therefore, is either not available to a
large segment of the industry or is inadequate for purposes of
improving the strength of the product throughout the sheet. The
latter factor is especially significant since paper failures during
printing, for example, are obviously disruptive to production
cycles and can be extremely costly.
[0005] A well-known method for increasing the strength of the paper
product, without surface sizing of a sheet, is by lamination.
Laminating is the process of applying a film to either one side or
both sides of a pressed paper product. Lamination has been found to
add stability to the sheet, allowing it to be more durable or stand
upright. There are two major lamination categories: pouch and roll.
Pouch lamination films are like envelopes and are sealed on one
edge. Roll lamination films can involve a process in which a layer
of film is applied to the front side of a document or it can
involve a process in which the document is sandwiched between two
layers and sealed by various lamination seal methods. The two most
common methods of lamination are thermal lamination, which requires
a heat source and pressure during the lamination process, and cold
lamination, in which only one side of a document is laminated. The
film used for cold lamination is much more costly than for thermal
lamination, but the equipment is known to be less expensive.
Additionally, cold lamination may not be as permanent as thermal
lamination. Regardless of the lamination type or process utilized,
lamination is known to be a costly method of adding strength to the
paper product. It requires additional equipment, sealants, and
films, and can introduce operational challenges to production time
and quality control. Additionally, the lamination layer or layers
contribute to the total finish caliper of the paper. Because total
finish caliper of the paper is also an important consumer
characteristic, processes which employ a lamination step are often
restricted to using lower basis weight paper.
[0006] Another method to increase the strength of a paper product
is through the addition of chemical additives directly to the fiber
furnish prior to forming the sheet. One such process is taught by
U.S. Pat. No. 5,328,567 to Kinsley, Jr. Common additives at the
wet-end of a paper machine, for example, include cationic starch or
melamine resins. The problem presented by these known wet-end
additives used in the papermaking industry, however, is their
inability to dramatically improve the mechanical properties of the
paper in the Z-direction, such as peel strength, surface pick
resistance and Scott internal bond. Another problem presented by
such known wet-end additives is their relatively low degree of
retention on the cellulose fiber during the initial formation of
the sheet, at the wet-end of the paper machine. In most
applications, significant portions of the wet-end additives
accompany the white water fraction as it drains through the wire.
This is due to high dilution and the extreme hydrodynamic forces
created at the slice of a Fourdrinier machine. Alternatively, a
significant portion of the additive may be lost in solution during
the dwell time between its addition to the stock and the subsequent
formation of the sheet on the machine. Accordingly, the use of
known methods for internally strengthening fiber products have not
produced a paper product with improved stiffness without the high
costs and operational challenges associated with a lamination
process.
[0007] Crosslinkers have been used in the paper-making industry.
For example, U.S. Pat. No. 5,281,307 to Smigo et al. uses a
crosslinking agent along with a polyvinyl alcohol/vinylamine
copolymer containing between 0.5 and 25 mole % vinylamine units to
improve certain properties of paper. In addition, GB Patent No.
1,471,226 relates to a process for the preparation of an aqueous
dispersion of modified cellulose fibers, which comprises the steps
of: (a) treating cellulose fibers, in aqueous dispersion, with a
crosslinking agent capable, on the application of heat, of
crosslinking cellulose fibers, (b) heating the dispersion to effect
at least partial crosslinking of the cellulose fibers, and (c)
treating the dispersion of at least partially crosslinked cellulose
fibers with a polymer containing hydroxyl and/or amino groups. The
desired paper product produced according to the '226 patent is to
minimize jamming in a copying machine and therefore has a basis
weight of preferably from 25 to 90 g/m 2 (i.e., 0.00512 lbs/ft 2 to
0.0184 lbs/ft 2).
[0008] U.S. Pat. No. 6,379,499 to Yang et al. discloses a method of
treating paper comprising: contacting the paper with a
hydroxy-containing polymer and a multifunctional aldehyde, in the
presence of a catalyst in some embodiments. The multifunctional
aldehyde may be gluteraldehyde, and the hydroxy-containing polymer
may be polyvinyl alcohol. Yang teaches a process in which the
multifunctional aldehyde and polyvinyl alcohol are pre-mixed (i.e.,
mixed together prior to their addition to the paper-making
process). The multifunctional aldehyde of Yang is used to at least
partially crosslink the polyvinyl alcohol, not the starch or pulp
fibers, before the multifunctional aldehyde and the polyvinyl
alcohol are added to the wet end pulp slurry. As Table 3 of Yang
shows, the pre-mixing and crosslinking of gluteraldehyde and
polyvinyl alcohol is necessary to retain or improve the dry
strength and folding endurance of the resulting paper in the
process according to Yang. With increased gluteraldehyde, however,
the folding endurance is significantly decreased as a detriment to
the desires of Yang. High amounts of multifunctional aldehydes have
generally be found to exhibit a loss of dry strength and decreased
folding endurance, which is in accordance with the findings of
Yang, but has now been employed to produce a rigid sheet while
retaining or improving stiffness.
[0009] U.S. Publication No. 2001/0051687 to Bazaj et al. and U.S.
Pat. No. 5,824,190 to Guerro et al. include small amounts of
crosslinker as an insolubilizer on the surface of the paper to
reduce the water solubility of the paper and improve printability.
In addition, Bazaj and Guerro require the addition of a hydrophobic
surface size and hydrophilic acrylamide polymer mixture. The
hydrophobic surface size and hydrophilic acrylamide polymer mixture
provides hydrophobicity to the surface of the paper to improve
printability by imparting substantial resistance to penetration of
ink and aqueous liquids to the paper.
[0010] While research into improving the mechanical properties of
the paper in the Z-direction, surface pick resistance, and Scott
internal bond remains on-going, there has recently been the
emergence of alkaline papermaking processes to solve other unmet
operational needs. Recent technologies employ a neutral or alkaline
papermaking process, which is carried out at pH 6 to 10, instead of
an acidic papermaking process. The neutral or alkaline papermaking
process has many advantages over known acidic processes, such as,
for example: (1) smaller energy utilization; (2) reduced corrosion
of machinery; and (3) environmental benefits associated with the
non-acidic white water system and waste stream.
[0011] In the conversion from acid papermaking to alkaline
papermaking, customers often complained that the resulting paper
product lost stiffness. Tests have shown that this loss was in the
rigidness of the paper sheet, not in the actual stiffness
measurements of the products. This is often described as a loss of
snap or rattle in the paper product. As is known in the art,
"rigidness" relates to the brittleness of a paper product (i.e.,
flexural stiffness or flexural rigidity), while "stiffness" relates
to the bending resistance of the paper product. A loss in rigidness
is an increase in the paper product's flexibility, but a loss in
stiffness is a decrease in the amount that the paper product
resists bending. To achieve a low thickness (e.g., low caliper)
paper product with the necessary stiffness and rigidity, paper
producers have had to thus far laminate sheets of lesser caliper
together. However, this adds a substantial and costly step to the
paper-making process and can not be utilized for all paper products
as lamination increases the overall basis weight of the paper
product.
SUMMARY OF THE INVENTION
[0012] It is highly desirable to utilize a papermaking process to
produce a paper product having the improved mechanical properties
of a laminated product in the Z-direction, such as peel strength,
surface pick resistance, and Scott internal bond, without a
lamination process. It is additionally desirable to utilize a
neutral or alkaline papermaking process to produce a paper product
with increased stiffness and rigidity, with higher basis weight, to
match existing laminated products without the added step and cost
of lamination. The non-laminated rigid sheet may additionally
possess increased dimensional stability, if such characteristic is
desired in the final paper product.
[0013] In one embodiment, the present invention provides a process
for making a stiffened and rigid paper which comprises: preparing a
pulp slurry consisting essentially of water, a cellulosic pulp, a
crosslinker, and a starch, and optionally a binder; draining the
liquid from the pulp slurry to form a web; and drying the web. The
crosslinker may be, for example, a glyoxal-containing crosslinker,
a gluteraldehyde, a polyfunctional aziridine, a
zirconium-containing crosslinker, a titanium-containing
crosslinker, and an epichlorohydrin, and mixtures thereof. When a
binder is included, the binder may be, for example, a starch,
casein, protein binder, carboxymethyl cellulose (CMC), polyvinyl
alcohol (PVOH), Gum product, and gelatin, and mixtures thereof.
[0014] In another embodiment of the present invention, a process
for making a stiffened and rigid paper consists essentially of:
preparing a pulp slurry consisting essentially of water, a
cellulosic pulp and a starch; draining the liquid from the pulp
slurry to form a web; adding at least one crosslinker; and drying
the web to produce a paper product. The crosslinker can be added at
various stages in the papermaking process. For example, the
crosslinker could be added to the wet end of the paper process by
spraying onto the web, by adding the crosslinker to the pulp in the
furnish, by adding the crosslinker at the size press, or adding
some of the crosslinker at multiple places to get the desired
properties.
[0015] The crosslinker is added in an amount effective to provide
an unlaminated sheet of paper having a comparable stiffness within
10% of, and a rigidity at least equal to, an equal caliper
laminated sheet for a basis weight in the range of 60 lbs/3300 ft 2
to 400 lbs/3300 ft 2. The amount of crosslinker preferably ranges
from about 0.3 weight percent to about 20 weight percent based on a
weight of total solids of the pulp slurry. In other words, the
present invention provides methods for making an unlaminated paper
product of a particular basis weight, wherein the unlaminated paper
product has comparable stiffness and equal or greater rigidity to
an equal caliper (i.e., equal thickness) laminated paper product
made of two or more lower basis weight papers laminated together by
any lamination method, such as dry lamination. Accordingly, the
present invention provides methods for making a paper product
having the improved mechanical properties of a laminated product in
the Z-direction, without a lamination step.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The present invention may be further understood with
reference to the following drawings:
[0017] FIG. 1 depicts a chart showing the effect on stiffness and
fold as the amount of crosslinker is increased from 0% to 25% to
50%; and
[0018] FIG. 2 shows a chart showing the effect on stiffness, fold,
and Water Cobb during a trial introducing 60 lbs. of crosslinker to
the process.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention provides a process for making a
stiffened and rigid paper. The processes of this invention utilize
crosslinkers as a main component, to produce paper products having
rigidness and stiffness comparable to a laminated sheet.
Embodiments of the present invention also provide methods to
produce a paper with similar mechanical strength characteristics of
a laminated product of equal caliper, but can utilize and produce
paper in a higher basis weight range than that which is used and/or
produced by known lamination processes. Processes which employ a
lamination step are often restricted to using lower basis weight
paper because the lamination layer(s) contribute to the total
finish caliper of the paper, an important consumer characteristic.
The present invention provides a process for making paper with
increased stiffness and rigidity, without a lamination process, and
can utilize and produce paper in a higher basis weight range since
there is no substantial addition to the total finish caliper of the
product by the present process.
[0020] An embodiment of the present invention provides a process
for making a stiffened and rigid paper, the process comprising the
steps of: (i) preparing a pulp slurry consisting essentially of
water, a cellulosic pulp, a crosslinker, and a starch; (ii)
draining the liquid from the pulp slurry to form a web; and (iii)
drying the web. The crosslinker can be added by any method known to
one skilled in the art such as, for example, spraying it onto the
web or adding it as a solution to the pulp slurry. The crosslinker
can be added at various stages in the papermaking process as well,
either in dry or wet form. For example, the crosslinker could be
added to the wet end of the paper process by spraying onto the web,
by adding the crosslinker to the pulp in the furnish, by adding the
crosslinker at the size press, or adding some of the crosslinker at
multiple places to get the desired properties. Thus, an alternative
embodiment of the present invention is a process for making a
stiffened and rigid paper consisting essentially of the steps of:
(i) preparing a pulp slurry consisting essentially of water, a
cellulosic pulp, and a starch; (ii) draining the liquid from the
pulp slurry to form a web; (iii) adding at least one crosslinker;
and (iv) drying the web.
[0021] The individual process steps of the present invention may be
carried out in any known manner using any suitable or conventional
paper making machine. For example, a Fourdrinier machine may be
used to carry out some or all of the steps of the present
invention. In addition, any suitable cellulosic pulp and starch may
be used in the present invention. The pulp is the basic
paper-making raw material and may be, for example, kraft pulp,
sulfite pulps, mechanical pulps, eucalyptus pulp or a myriad of
recycled pulps, among others. The starch is used to increase the
stiffness and rigidness of the paper, as well as increase the Scott
internal bond. The starch may be, for example, an ethylated starch,
oxidized starch, waxy maize, or pearl starch, among others.
[0022] The crosslinker is preferably added in amounts of about 0.3
weight percent or greater, about 0.5 weight percent or greater,
about 1.5 weight percent or greater, about 3 weight percent or
greater, or about 10 weight percent or greater, based on the weight
of the total solids. For example, in representative embodiments the
crosslinker may be present in an amount between about 0.3 weight
percent and about 20 weight percent, 0.3 weight percent and about
10 weight percent, between about 1.5 weight percent and about 20
weight percent, between about 0.5 weight percent and about 10
weight percent, about 1.5 weight percent and about 10 weight
percent, between about 3 weight percent and about 20 weight
percent, between about 3 weight percent and about 10 weight
percent, based on the weight of the solids in the pulp slurry.
[0023] The addition of the crosslinker at individual stages may be
determined by whether the crosslinker selected is cationic or not.
For example, the crosslinker is preferably sprayed onto the web if
it is not cationic and is preferably added to the pulp in the
furnish if it is cationic. When the crosslinker is applied by
spray, the crosslinker is between about 0.3 weight percent and
about 20 weight percent, and preferably between about 1.5 weight
percent and about 10 weight percent, based on the weight of the
total solids. When the crosslinker is present in the pulp slurry,
the crosslinker may be between about 0.3 weight percent and about
20 weight percent, between about 0.3 weight percent and about 10
weight percent, between about 1.5 weight percent and about 20
weight percent, or between about 0.5 weight percent and about 5
weight percent, based on the weight of the solids in the pulp
slurry. The weight percent determination depends, in part, on the
nature of the crosslinker and the properties (e.g., rigidness and
stiffness) to be achieved and can readily be empirically made.
[0024] In addition, different types of crosslinkers can be utilized
and added at various stages in the process. For example, one type
of crosslinker could be added at the wet end and another type at
the size press to achieve the desired properties. Effective
crosslinkers may include a glyoxal-containing crosslinker, a
gluteraldehyde, a polyfunctional aziridine, a zirconium-containing
crosslinker, a titanium-containing crosslinker, and an
epichlorohydrin, and mixtures thereof. The crosslinker functions to
bind the pulp materials together, including at least a portion of
the fibers, to greatly increase the sheet stiffness and rigidness
and produce a product with mechanical properties comparable to a
laminated sheet. Depending on the stage at which the crosslinker is
added, the crosslinking may be cured by various downstream stages.
For example, the crosslinking may be fully cured by the heat of the
rolls in the dry end of the papermaking process. Similarly, the
crosslinking may be cured in the heat cycle at the coater, if the
sheet is to be coated for the final product. Without wishing to be
bound by a particular theory, the crosslinking may function to
crosslink the fibers, the starch, or both. For example, when the
crosslinker is added at the wet end, the fibers themselves may be
crosslinked, and when the crosslinker is added at the size press,
the fibers as well as the starch may be crosslinked.
[0025] The process of the present invention may further comprise
the step of adding a binder to either the pulp slurry of the water,
the cellulosic pulp, the crosslinker, and the starch. Binders can
be added to obtain the desired finished properties or help balance
the level of rigidness with the needed stiffness level for paper
produced by this invention. For example, starches, casein, or other
protein binders can be used if more rigidness is needed with the
stiffness. Protein binders can affect the mechanical properties of
the product, such as, for example, causing the sheet to become more
brittle or rigid. The brittleness and stiffness can be adjusted to
achieve the desired mechanical properties of the final paper
product. For example, other polymers may be added to the process if
more flexibility is needed to balance brittleness while obtaining
or maintaining a desired stiffness. Such polymers may include, for
example, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVOH),
various Gum products, and gelatins (either anionic and/or
cationic). As is known to one having ordinary skill in the art, the
viscosity of such polymers may vary depending on the desired
characteristics of the final product. Depending on the binder
employed, the binder may be between about 0.1 weight percent and
about 5 weight percent, and preferably between about 1 weight
percent and about 2.5 weight percent, based on the weight of the
total solids. It is to be understood that the material components
of the present invention may be added in any form known in the art.
The components may be added as, for example, part of an aqueous
solution or as a dry powder.
[0026] The process of the present invention may further comprise
the step of adding a common papermaking additive, for example, to
the pulp slurry or the web (e.g., at the size press). Typical or
traditional papermaking additives known in the art, include but are
not limited to, retention aids, drainage aids, flocculants, dyes,
dye fixatives, inks, colorants, whiteners, brighteners, opacifiers
(such as TiO.sub.2 or calcium carbonate), fillers (such as chalk or
china clay), perfumes, microorganism control agents, agents for
controlling non-biological deposits, alum, internal sizing agents
(such as alkylketene dimer, alkenyl succinic anhydride, or rosin
size), foam control agents, pH control agents, and mixtures
thereof. Such traditional papermaking additives are well known to
one of ordinary skill in the art. The addition of a hydrophilic
polyacrylamide to the size press in combination with a hydrophobic
surface sizing agent is not traditional and, therefore, would not
be included. In particular, the process does not include the use of
hydrophilic polyacrylamides in a mixture with hydrophobic surface
size agents at the size press, for example, as described in Bazaj
and Guerro, which influence the hydrophobicity or resistance to
penetration by water or aqueous substances of the paper. Use of a
hydrophobic surface sizing agent without the addition of a
hydrophilic polyacrylamide at the size press is well known and
would be included as a traditional papermaking additive.
[0027] When a Fourdrinier machine is employed for the papermaking
process, the material components of the present invention can be
added to the process at the wet end of the process. Specifically,
the material components may be added to the process at, for
example, the head box, immediately after the slice, onto the web,
at the couch roll, or at the size press. The components can be
added by a variety of methods known in the art such as, for
example, by spraying or adding as a solution or slurry. The
components may be added together or separately, and the components
may be added at separate stages in the process. The components
themselves and the location, quantity, method, and order of their
addition may be determined based on the properties desired in the
final paper product. As illustrated by the Examples below, the
following trends, for example, can be inferred: (1) improved
stiffness and rigidness can be seen as inversely related to
decreased tensile, tear, and fold properties; (2) the greatest
improvement to stiffness and rigidity can be attributed to the
addition of a crosslinker and higher amounts of crosslinker
produced greater results; (3) the addition of further polymers and
additives, such as polyvinyl alcohol and carboxymethyl cellulose,
may be employed to balance the desired flexibility, rigidness, and
stiffness of the final paper product; (4) the crosslinker may be
added at various stages in the process such as, for example, at the
size press and/or the wet end, to produce a paper product with
improved stiffness and rigidity; and (5) the present invention can
utilize and produce paper in a higher basis weight range since
there is no substantial addition to the total finish caliper of the
product.
[0028] Paper produced by the processes of the present invention has
various mechanical properties. The present invention provides a
process to produce a paper product having increased stiffness and
rigidness. These mechanical properties of the paper product, as
well as others, are analyzed using a variety of tests known in the
art. Many of these tests are established, collected, and unified by
TAPPI, the leading association for the worldwide pulp, paper,
packaging, and converting industries. Two commonly known methods
for evaluating the bending resistance or stiffness of paper
products are described by TAPPI Method T 489, which utilizes a
Taber-type tester in its basic configuration, and by TAPPI Method T
543, which utilizes a Gurley-type tester.
[0029] Both commonly known methods for measuring stiffness utilize
a balanced pendulum or pointer which is center-pivoted and can be
weighted at three points below its center. The pointer moves freely
in both left and right directions on cylindrical jewel bearings
which make the mechanism highly sensitive, even to light-weighted
materials. A sample specimen of a specific size is mounted on the
Stiffness Tester using a specimen clamp. Located on the pendulum,
the lower faces of the specimen clamp jaws are exactly on the
center of rotation. This ensures a constant test length and
deflection angle for accurate and repeatable results. Both jaws of
the specimen clamp are adjustable, so the test specimen can be
positioned precisely in the center regardless of material
thickness. The clamp is located on one of several positions on a
motorized arm which also moves left and right. The bottom 0.25'' of
the sample overlaps the top of the pointer (a triangular shaped
"vane"). During the test, the sample is moved against the top edge
of the vane, moving the pendulum until the sample bends and
releases it. In a Taber apparatus, force is applied to the lower
end of the specimen by a pair of rollers. The rollers, which are
attached to a driving disc located directly behind the pendulum,
push against the test specimen and deflect it from its vertical
position. The pendulum applies increasing torque to the specimen as
it deflects further from its original position.
[0030] The Gurley unit is a measure of the stiffness of a material.
As described above, the measurement device holds a piece of
material vertically and tests the force required to deflect the
material a specified amount. One Gurley unit is equivalent to one
milligram of force (mgf). A related unit, the Taber, is highly
correlated but uses a different apparatus (manufactured by Taber
Industries) for performing measurements. The Taber apparatus shows
results in Taber units, with each Taber unit equivalent to one
gram-centimeter (g-cm). Because the Taber and Gurley apparatuses
vary in their methods and analysis units, a conversion equation has
been identified which correlates one Taber unit equal to 0.01419
Gurley units, minus 0.935 (T=0.01419 G-0.935). Accordingly, 20-150
g-cm units on the Taber correspond to roughly 2,000-10,000 mgf
Gurley stiffness units.
[0031] Tests which measure the tensile properties are also utilized
in evaluating paper products. The tensile properties of paper are
closely linked to the randomly deposited fiber network. A number of
parameters, which incorporate such factors as the basis weight of
the sheet, the coarseness of the fibers (mass per unit length), and
width of the fibers, can be derived to describe the random network
formed by the fibers. Other factors will influence the tensile
characteristics of the sheet, including the strength of the
individual fibers and the strength of the bonds. Two commonly used
tests which utilize these factors to measure tensile properties of
paper products are Tensile Energy Absorption (TEA) and Scott-type
Internal Bond Strength (SIB). A TEA test, in accordance with TAPPI
Method T 404 (using a pendulum-type tester) or T 494 (using a
constant rate elongation apparatus), measures in pounds per square
feet (lb/ft 2) the amount of energy required to fracture a
specimen. It is normalized to the surface area of the specimen
tested. A higher TEA equates to a tougher paper sheet. Other known
methods for performing a TEA test are as taught by the ASTM D828,
ISO 1924, and SCAN P38 standards. The TEA test is often used to
measure and describe the properties of the paper in the machine
direction (MD). The SIB test, in accordance with TAPPI Method T
569, measures the energy absorption and peeling strength of the
paper product specimens, sized as card boards, as they are impacted
by a specified load at a certain angle. The "Z" directional rupture
is initiated by the impact of a pendulum having both a controlled
mass and a controlled velocity that exceeds 6000 times the velocity
of tensile strength and other dead-weight testers. The geometry of
the apparatus causes the tensile stress to be rotational in nature
with negligible shear stress on the specimen. Because energy is
absorbed during the elongation and stretching of the sample's fiber
network prior to rupture, this internal bond test responds to the
semi-elastic nature of paper and paperboard. The test is a
measurement of strain energy per unit sample area, which is
proportional to the area under the stress-strain curve. The SIB
test is often used to measure and describe the properties of the
paper in the cross direction (CD).
[0032] The Mullen burst strength test is another technique for
evaluating the tensile properties of paper, specifically those
properties associated with the tear resistance strength of the
paper. It is also well known to be an indication of the puncture
resistance of the paper sheet. The burst test, according to TAPPI T
403, involves clamping a paper sheet with an annular clamp and then
pressurizing a rubber diaphragm behind the paper until it ruptures.
Since the sheet may emit an audible "pop," the test is also
commonly referred to as the "pop test." A uniform strain is applied
to the paper sheet in both the machine and cross machine
directions. Therefore, the direction with the lower breaking strain
will fail first. This direction is typically the machine
direction.
[0033] In addition to the above test methods which analyze the
tensile properties and the flexural stiffness of paper products,
other tests may be used to measure the edgewise compression
strength of the paper. One of the primary uses for paper is as
packaging material. Paper boxes are often loaded edgewise
especially when being stacked. Therefore, it is important to
evaluate and control the edgewise compression characteristics of
paper. Out-of-plane buckling of the paper sheet, under a given
stress, helps to identify the edgewise failure threshold of the
paper product. This is particularly true for longer spans of paper
than for shorter spans, because longer spans will exhibit a lower
compressive strength than short spans. Also, because out-of-plane
buckling occurs during edgewise loading, the bending stiffness and
long span compression are closely related. The span length can be
better defined by a slenderness ratio, which is a ratio of the span
length to sample thickness. The various test methods that are
available use different slenderness ratios. Therefore, it is
important to be aware of the test method used to determine the
edgewise compressive strength and its relationship to the
particular application. Two commonly used methods known in the art
for edgewise compression testing include Ring Crush Testing (RCT)
and STFI Short-span compression testing (STFI). Analysis by RCT,
according to TAPPI T 818 and T 822, involves a process in which a
short cylinder of material is inserted into an annular groove and
axially loaded to failure. Results from the RCT analysis are quoted
in units of force, such as kN/m. STFI testing measures the
compression strength of paper and board materials over a very short
compression span. The clamping arrangement for STFI, according to
TAPPI T 826, is designed to prevent the test piece from buckling
during the test.
[0034] The double-fold folding endurance (i.e., M.I.T. folding
endurance) of paper products is also often tested, as is known in
the art. Folding endurance is the capability of the paper product
to withstand multiple folds before it breaks. It is defined as the
number of double folds that a strip of 15 mm wide and 100 mm length
can withstand, under a specified load, before it breaks. The M.I.T.
tester for folding endurance, according to TAPPI T 511, is well
known in the art. Folding endurance has been useful in measuring
the deterioration of paper upon aging. It is important for printing
grades where the paper is subjected to multiple folds like in
books, maps, or pamphlets. Long and flexible fibers are believed to
provide high folding endurance. Rigid sheets have low M.I.T.
folding endurance measurements as these type of sheets have very
little stretch in the sheet.
[0035] A key concept of the embodiments of the present invention is
that they produce a more rigid and stiff paper product than prior
art processes, without the need for a lamination layer. This
characteristic is shown by the results of, for example, the Gurley
stiffness test, the M.I.T. folding endurance, the Ring Crush Test,
and/or the STFI short span compression test. Thus, in an embodiment
of the invention, the crosslinker is added in an amount effective
to provide an unlaminated sheet of paper having a comparable
stiffness within 10% of, and a rigidity at least equal to, an equal
caliper laminated sheet. In other words, the present invention
provides methods for making an unlaminated paper product of a
particular basis weight, wherein the unlaminated paper product has
comparable stiffness and equal or greater rigidity to an equal
caliper (i.e., equal thickness) laminated paper product made of two
or more lower basis weight papers laminated together by any
lamination method, such as dry lamination. More generally, the
present invention is directed to producing paper for applications
requiring increased rigidness and stiffness, such as cards, playing
cards, or boxes, among others, and preferably has a basis weight of
at least about 60 lbs/3300 ft 2 to about 400 lbs/3300 ft 2.
[0036] In achieving the production of a more rigid paper product,
without the use of a lamination process, other mechanical
properties of the paper may be maintained or reduced, as is known
to one skilled in the art. For example, the mechanical strength
properties of tensile, stretch, tear, and fold may decrease as they
are often properties that are contrary to the indication of a more
rigid sheet. An increase in rigidness can be seen as an increase in
the brittleness of the sheet, which can be identified by a decrease
in the M.I.T. double-fold folding endurance test results. The
results of the Tensile Energy Absorption (TEA) and Scott-type
Internal Bond (SIB) tests may similarly be evaluated to indicate
that a more rigid sheet was produced. Maintained or decreased
results for these tests may inversely relate to improved rigidity
of the paper product, as shown by more direct stiffness tests.
[0037] It was also surprisingly found that adding higher amounts of
crosslinker, for example, ranging from about 0.3 weight percent to
about 20 weight percent based on a weight of total solids of the
pulp slurry, increases the amount of water penetration or
absorption of water or other aqueous substances into the surface of
the paper. In other words, water is absorbed easier into the
surface of the paper when crosslinker is included in the process
than in the case when no crosslinker is added to the paper. The
easier absorption or penetration of water may be beneficial in the
present invention. For example, increased absorption or penetration
may be beneficial in downstream coating processes where a liquid
coating may need to absorb or penetrate into the sheet.
[0038] The paper product may have a high water Cobb value, which is
suggestive of the capacity of water that the paper is able to
absorb. The water Cobb value is the mass of water in grams that
absorbs into one square meter of paper in two minutes time. The
water Cobb value may be determined routinely by those skilled in
the art, for example, by following TAPPI test method T 441, Water
Absorptiveness of sized (non-bibulous) paper, paperboard, and
corrugated fiberboard (Cobb test). Thus, a high water Cobb value
indicates the ability to absorb water, whereas a low water Cobb
value indicates resistance to absorbing water. When the crosslinker
is added, the paper product may exhibit a high water Cobb value of
greater than 50, greater than 100, or greater than 200, for
example. In particular, with high amounts of crosslinker, the water
Cobb value may range from about 50 to about 500, about 100 to about
400, about 200 to about 300, about 210 to about 260, or about 220
to about 250.
[0039] Embodiments of the present invention provide a process for
making a paper with increased stiffness and rigidity, as shown in
the following examples. The processes of this invention utilize
crosslinkers as a main component, to produce paper products having
increased rigidness and stiffness comparable to a laminated sheet.
As rigidness and stiffness have been identified as important
characteristics for particular products, the embodiments of the
present invention provide methods to produce paper products in
which these characteristics are enhanced while other
characteristics may be maintained or reduced. The examples below
show various embodiments of the present invention which produce
paper products with similar mechanical strength characteristics of
a laminated product of equal caliper, but which can utilize and
produce paper in a higher basis weight range than that which is
used and/or produced by known lamination processes. The processes
of the present invention were tested to produce paper products
having three target freeness levels: 200, 350, and 500 ml C.S.F.
Freeness, measured in units of Canadian Standard Freeness (C.S.F.),
is a term used to define how quickly water is drained from the
pulp. The opposite of freeness is slowness. Freeness or slowness is
the function of beating or refining, as is known in the art.
Additionally, the processes of the present invention were tested to
produce paper products having three target basis weights: 65
lbs/3000 ft 2, 115 lbs/3000 ft 2, and 165 lbs/3000 ft 2.
EXAMPLES
[0040] The following examples are included to more clearly
demonstrate the overall nature of the present invention. Examples
1, 2, and 3 illustrate the improved results obtained by employing
the papermaking processes of this invention. The Examples
illustrate the products which may be obtained, and the properties
which may be achieved, according to the embodiments of the present
invention. The Examples below describe processes in which various
components are added at various stages of the papermaking process,
in accordance with the embodiments of the present invention. In
addition to a base pulp slurry, the examples describe sample
formulations which include a starch. For example, a hydroxyethyl
starch sold by Penford Products Co. under the trade name "PENFORD
GUM 280" or "PENFORD GUM 290" was employed in the sample
formulations. A crosslinker, such as a Glyoxal-containing
crosslinker sold by BASF under the trade name "CURESAN" and/or a
polyamide-epichlorohydrin crosslinker sold by Ashland Hercules
under the trade name "POLYCUP 172," is employed in a number of
sample formulations. Additionally, in accordance with various
embodiments of the present invention, various sample formulations
include a polyvinyl alcohol, such as that sold by Celanese
Corporation under the trade name "CELVOL," and/or a
carboxymethylcellulose (CMC), such as that sold by Ashland Hercules
under the trade name "CMC 7MCT."
Example 1
[0041] A first sample set was tested with a target refining
freeness of 200 ml C.S.F. and a target basis weight of 65 lbs/3000
ft 2. The following sample processes were tested: [0042] A1: A
control paper product manufactured by adding only 60 lbs of PENFORD
GUM 290 hydroxyethyl starch per ton of dry paper pulp at the size
press. [0043] A2: A paper product manufactured by adding 60 lbs of
PENFORD GUM 290 hydroxyethyl starch per ton of dry paper pulp at
the size press and 6 lbs POLYCUP 172 polyamide-epichlorohydrin
crosslinker at the couch roll. [0044] A3: A paper product
manufactured by adding 60 lbs of PENFORD GUM 290 hydroxyethyl
starch per ton of dry paper pulp at the size press and 6 lbs of
CURESAN 200 Glyoxal-containing crosslinker per ton of dry paper
pulp at the couch roll. [0045] A4: A paper product manufactured by
adding 60 lbs of PENFORD GUM 290 hydroxyethyl starch per ton of dry
paper pulp at the couch roll and 60 lbs of CURESAN 200
Glyoxal-containing crosslinker per ton of dry paper pulp at the
size press. [0046] A5: A paper product manufactured by adding 50
lbs of CELVOL 165S polyvinyl alcohol per ton of dry paper pulp to
the pulp slurry, 60 lbs of PENFORD GUM 290 hydroxyethyl starch per
ton of dry paper pulp at the size press, and 60 lbs of CURESAN 200
Glyoxal-containing crosslinker per ton of dry paper pulp at the
size press. [0047] A6: A paper product manufactured by adding 50
lbs of CELVOL 165S polyvinyl alcohol per ton of dry paper pulp to
the pulp slurry, and 60 lbs of PENFORD GUM 290 hydroxyethyl starch
per ton of dry paper pulp at the size press and 200 lbs of CURESAN
200 Glyoxal-containing crosslinker per ton of dry paper pulp at the
couch roll. [0048] A7: A paper product manufactured by adding 60
lbs of CURESAN 200 Glyoxal-containing crosslinker per ton of dry
paper pulp at the couch roll and 30 lbs of CELVOL 165S per ton of
dry paper pulp at the size press.
[0049] The sample paper products manufactured according to the
processes described above were then analyzed using the tests
described above, in accordance with their respective TAPPI
standards. Table 1 below shows the results of these tests:
TABLE-US-00001 TABLE 1 Paper products produced according to
embodiments of the present invention, with a target refining
freeness of 200 ml C.S.F. and a target basis weight of 65 lbs/3000
ft{circumflex over ( )}2. MD DRY CD DRY M.I.T. TEA Stretch FOLD
STFI Ring Crush Dry Tensile Gurley in lb/sq ft Ft/lbs/sq in no. dbl
fold Normalized Normalized Normalized Normalized Normalized
Stiffness Sample Mean Mean Mean Geo. Mean Density Geo. Mean Density
Geo. Mean Normalized A1 172.79 6.89 100.80 10.81 9.61 40.192 35.753
32.75 329.405 A2 168.38 7.30 92.40 11.01 10.64 43.657 42.167 32.64
365.499 A3 153.76 7.22 95.20 11.13 10.78 44.038 42.672 33.03
361.586 A4 129.81 5.18 6.30 12.74 11.49 49.339 44.498 32.68 369.775
A5 139.03 5.34 7.70 12.81 11.66 50.812 46.225 33.66 381.039 A6
120.39 4.40 1.00 12.48 12.34 49.331 48.799 31.37 406.489 A7 166.22
7.22 67.40 11.75 10.47 42.512 37.863 34.22 331.422
[0050] Table 1 shows the results of the test samples which target a
refining freeness of 200 ml C.S.F. and a basis weight of 65
lbs/3000 ft 2. All of the tests samples in this sample set showed
an improved stiffness and rigidity over the control A1 sample,
which was a control paper product manufactured by adding only 60
lbs of PENFORD GUM 290 hydroxyethyl starch per ton of dry paper
pulp to the fiber pulp web at the size press. While sample paper
products A2-A7 all showed improved stiffness and rigidity
measurements, the test product manufactured according to the A6
process showed the best results at this refining freeness and basis
weight. The A6 process manufactured a paper product by adding 50
lbs of CELVOL 165S polyvinyl alcohol per ton of dry paper pulp to
the pulp slurry, and 60 lbs of PENFORD GUM 290 hydroxyethyl starch
per ton of dry paper pulp at the size press and 200 lbs of CURESAN
200 Glyoxal-containing crosslinker per ton of dry paper pulp at the
couch roll. This sample product presented the best combination of
performance metrics from the Ring Crush Test, STFI test, and Gurley
Stiffness test, as can be seen in Table 1 above. As described
above, the improved stiffness and rigidness can be seen as
inversely related to decreased tensile, tear, and fold properties
shown by the TEA, SIB, and M.I.T. tests in Table 1.
[0051] When the crosslinker is alternatively added at the size
press instead of at the couch roll, as it is in the A5 process, the
process still produced a paper product with improved stiffness and
rigidity when compared to the product of the control A1 process.
Additionally, as the A7 process shows, the polyvinyl alcohol may be
added at the size press instead of to the pulp slurry. The A7
process configuration shows that the stiffness and rigidity may be
improved while retaining tensile, stretch, and fold properties
comparable to the control A1 process. Accordingly, the components
themselves and the location, quantity, method, and order of their
addition may be adjusted based on the properties desired in the
final paper product.
Example 2
[0052] Another sample set was tested with a target refining
freeness of 350 ml C.S.F. and a target basis weight of 115 lbs/3000
ft 2. The following sample processes were tested: [0053] B1: A
control paper product manufactured by adding only 60 lbs of PENFORD
GUM 280 hydroxyethyl starch per ton of dry paper pulp at the size
press. [0054] B2: A paper product manufactured by adding 30 lbs
CELVOL 165S polyvinyl alcohol to the pulp slurry and 60 lbs of
PENFORD GUM 280 hydroxyethyl starch per ton of dry paper pulp at
the size press. [0055] B3: A paper product manufactured by adding
50 lbs of CELVOL 165S polyvinyl alcohol per ton of dry paper pulp
to the pulp slurry and 60 lbs of PENFORD GUM 280 hydroxyethyl
starch per ton of dry paper pulp at the size press. [0056] B4: A
control paper product manufactured by adding only 60 lbs of PENFORD
GUM 280 hydroxyethyl starch per ton of dry paper pulp at the size
press. [0057] B5: A paper product manufactured by adding 25 lbs of
CMC 7MCT carboxymethylcellulose per ton of dry paper pulp to the
pulp slurry and 60 lbs of PENFORD GUM 280 hydroxyethyl starch per
ton of dry paper pulp at the size press. [0058] B6: A paper product
manufactured by adding 50 lbs of CMC 7MCT carboxymethylcellulose
per ton of dry paper pulp to the pulp slurry and 60 lbs of PENFORD
GUM 280 hydroxyethyl starch per ton of dry paper pulp at the size
press. [0059] B7: A control paper product manufactured by adding
200 lbs of water per ton of dry paper pulp at the couch roll and 60
lbs of PENFORD GUM 280 hydroxyethyl starch per ton of dry paper
pulp at the size press. [0060] B8: A paper product manufactured by
adding 200 lbs of CURESAN 200 Glyoxal-containing crosslinker per
ton of dry paper pulp at the couch roll and 60 lbs of PENFORD GUM
280 hydroxyethyl starch per ton of dry paper pulp at the size
press. [0061] B9: A paper product manufactured by adding 25 lbs of
CELVOL 165S polyvinyl alcohol per ton of dry paper pulp to the pulp
slurry, 200 lbs of CURESAN 200 Glyoxal-containing crosslinker per
ton of dry paper pulp at the couch roll, and 60 lbs of PENFORD GUM
280 hydroxyethyl starch per ton of dry paper pulp at the size
press. [0062] B10: A paper product manufactured by adding 25 lbs of
CMC 7MCT carboxymethylcellulose per ton of dry paper pulp to the
pulp slurry, 200 lbs of CURESAN 200 Glyoxal-containing crosslinker
per ton of dry paper pulp at the couch roll, and 60 lbs of PENFORD
GUM 280 hydroxyethyl starch per ton of dry paper pulp at the size
press.
[0063] The sample paper products manufactured according to the
processes described in Example 2 were then analyzed using the tests
described above, in accordance with their respective TAPPI
standards. Table 2 below shows the results of these tests:
TABLE-US-00002 TABLE 2 Paper products produced according to
embodiments of the present invention, with a target refining
freeness of 350 ml C.S.F. and a target basis weight of 115 lbs/3000
ft{circumflex over ( )}2. MD DRY CD DRY M.I.T. TEA stretch FOLD
STFI Ring Crush Dry Tensile Gurley in lb/sq ft Percent no. dbl fold
Normalized Normalized Normalized Normalized Normalized Stiffness
Sample Mean Mean Mean Geo. Mean Density Geo. Mean Density Geo. Mean
Normalized B1 273.77 7.64 78.10 17.68 15.34 91.459 79.370 52.39
1609.752 B2 268.46 7.58 80.30 18.04 15.54 92.562 79.768 53.43
1669.286 B3 273.23 7.33 81.70 18.10 15.67 94.260 81.583 53.97
1624.682 B4 281.94 7.71 91.90 17.90 15.38 91.365 78.481 53.10
1566.051 B5 352.58 7.80 96.60 19.13 16.39 99.865 85.560 59.21
1658.038 B6 367.46 8.13 115.80 19.24 16.25 100.448 84.850 60.80
1669.448 B7 292.53 7.44 57.90 17.78 15.24 96.864 83.012 56.16
1638.309 B8 159.15 4.39 0.00 21.71 19.34 123.628 110.129 53.90
1990.019 B9 172.77 4.10 0.00 21.69 19.19 116.647 103.208 53.59
1972.528 B10 209.46 4.54 0.00 23.38 19.40 128.430 106.525 59.49
1902.573
[0064] Table 2 shows the results of the test samples which target a
refining freeness of 350 ml C.S.F. and a basis weight of 115
lbs/3000 ft 2. In addition to showing the effects of the various
stages for addition of the components on the resulting paper
product properties, these tests further show the impact that
polyvinyl alcohol, carboxymethyl cellulose, and the
Glyoxal-containing crosslinker individually have on the products.
Control processes B1 and B4 manufactured a paper product by adding
only 60 lbs of PENFORD GUM 290 hydroxyethyl starch per ton of dry
paper pulp to the fiber pulp web at the size press. Control process
B7 manufactured a paper product by adding 200 lbs of water per ton
of dry paper pulp at the couch roll and 60 lbs of PENFORD GUM 280
hydroxyethyl starch per ton of dry paper pulp at the size press.
Processes B2 and B3 added varying amounts of polyvinyl alcohol to
the pulp slurry, and showed improved stiffness and rigidity
measurements over the product of process B1. Processes B5 and B6
added varying amounts of carboxymethyl cellulose to the pulp
slurry, and also showed improved stiffness and rigidity
measurements over the product of process B4. The greatest
improvements to the stiffness and rigidity of the paper products,
however, were seen in products produced according to processes B8,
B9, and B10, all of which contained the crosslinker.
[0065] Processes B9 and B10 added polyvinyl alcohol and
carboxymethyl cellulose to the crosslinker, respectively. As shown
by the results of process B8 in Table 2, however, the greatest
improvement to stiffness and rigidity can be attributed to the
addition of the crosslinker. As discussed above, the improved
stiffness and rigidness can be seen as inversely related to
decreased tensile, elongation, and fold properties shown by the
TEA, Stretch, and M.I.T. Fold tests in Table 2. The processes of B9
and B10, which add polyvinyl alcohol and carboxymethyl cellulose to
the crosslinker, respectively, show favorable rigidity and
stiffness results and also retain some of the tensile, stretch, and
fold properties in the paper product. Accordingly, while the
addition of a crosslinker offers significant gains to the stiffness
and rigidity of the paper product, the addition of further polymers
and additives may be employed to balance the desired flexibility,
rigidness, and stiffness of the final paper product.
Example 3
[0066] A further sample set was tested with a target refining
freeness of 500 ml C.S.F. Two target basis weights were tested for
this sample set: a first subset including samples C1-C6 with the
target basis weight of 165 lbs/3000 ft 2 and a second subset
including samples C7-C9 with the target basis weight of 65 lbs/3000
ft 2. The following sample processes were tested: [0067] C1: A
control paper product manufactured by adding only 60 lbs of PENFORD
GUM 280 hydroxyethyl starch per ton of dry paper pulp at the size
press. [0068] C2: A paper product manufactured by adding 60 lbs of
PENFORD GUM 280 hydroxyethyl starch per ton of dry paper pulp at
the size press and 6 lbs of CURESAN 200 Glyoxal-containing
crosslinker per ton of dry paper pulp at the couch roll. [0069] C3:
A paper product manufactured by adding 60 lbs of PENFORD GUM 280
hydroxyethyl starch per ton of dry paper pulp at the size press and
200 lbs of CURESAN 200 Glyoxal-containing crosslinker per ton of
dry paper pulp at the couch roll. [0070] C4: A paper product
manufactured by adding 50 lbs of CELVOL 165S polyvinyl alcohol per
ton of dry paper pulp to the pulp slurry, 200 lbs of CURESAN 200
Glyoxal-containing crosslinker per ton of dry paper pulp at the
couch roll, and 60 lbs of PENFORD GUM 280 hydroxyethyl starch per
ton of dry paper pulp at the size press. [0071] C5: A paper product
manufactured by adding 50 lbs of CELVOL 165S polyvinyl alcohol per
ton of dry paper pulp to the pulp slurry, and 6 lbs of CURESAN 200
Glyoxal-containing crosslinker per ton of dry paper pulp at the
couch roll and 60 lbs of PENFORD GUM 280 hydroxyethyl starch per
ton of dry paper pulp at the size press. [0072] C6: A paper product
manufactured by adding 50 lbs of CELVOL 165S polyvinyl alcohol per
ton of dry paper pulp to the pulp slurry, 6 lbs of POLYCUP 172
polyamide-epichlorohydrin crosslinker per ton of dry paper pulp at
the couch roll, and 60 lbs of PENFORD GUM 280 hydroxyethyl starch
per ton of dry paper pulp at the size press. [0073] C7: A paper
product with the target basis weight of 65 lbs/3000 ft 2
manufactured by adding 60 lbs of PENFORD GUM 280 hydroxyethyl
starch per ton of dry paper pulp at the size press and 6 lbs of
CURESAN 200 Glyoxal-containing crosslinker per ton of dry paper
pulp at the couch roll. [0074] C8: A paper product with the target
basis weight of 65 lbs/3000 ft 2 manufactured by adding 50 lbs of
CELVOL 165S polyvinyl alcohol per ton of dry paper pulp to the pulp
slurry, and 6 lbs of CURESAN 200 Glyoxal-containing crosslinker per
ton of dry paper pulp at the couch roll and 60 lbs of PENFORD GUM
280 hydroxyethyl starch per ton of dry paper pulp at the size
press. [0075] C9: A paper product with the target basis weight of
65 lbs/3000 ft 2 manufactured by adding 50 lbs of CELVOL 165S
polyvinyl alcohol per ton of dry paper pulp to the pulp slurry, 6
lbs of POLYCUP 172 polyamide-epichlorohydrin crosslinker per ton of
dry paper pulp at the couch roll, and 60 lbs of PENFORD GUM 280
hydroxyethyl starch per ton of dry paper pulp at the size
press.
[0076] The sample paper products manufactured according to the
processes described in Example 3 were then analyzed using the tests
described above, in accordance with their respective TAPPI
standards. Table 3 below shows the results of these tests:
TABLE-US-00003 TABLE 3 Paper products produced according to
embodiments of the present invention, with a target refining
freeness of 500 ml C.S.F. Samples C1-C6 have a target basis weight
of 165 lbs/3000 ft{circumflex over ( )}2 and samples C7-C9 have a
the target basis weight of 65 lbs/3000 ft{circumflex over ( )}2. MD
DRY CD DRY M.I.T. TEA stretch FOLD STFI Ring Crush Dry Tensile
Gurley in lb/sq ft Percent no. dbl fold Normalized Normalized
Normalized Normalized Normalized Stiffness Sample Mean Mean Mean
Geo. Mean Density Geo. Mean Density Geo. Mean Normalized C1 130.33
4.32 30.00 17.13 16.79 93.294 91.422 48.98 4253.601 C2 150.39 4.87
43.44 18.23 17.38 103.477 98.615 54.18 4422.724 C3 93.05 2.70 1.00
20.04 19.30 110.252 106.217 52.97 4747.070 C4 131.02 3.37 0.80
23.11 22.07 128.978 123.226 61.63 4633.489 C5 161.57 4.81 38.10
20.05 18.27 113.117 103.068 58.87 4269.304 C6 166.15 5.16 42.80
19.31 18.25 108.862 102.889 57.36 4434.834 C7 51.61 3.39 22.90 7.16
7.56 32.373 34.144 20.68 388.444 C8 55.44 3.49 31.70 7.65 8.18
33.832 36.209 22.20 395.993 C9 53.83 2.65 3.30 8.85 9.21 70.926
41.812 24.22 408.804
[0077] Table 3 shows the results of the test samples which target a
refining freeness of 500 ml C.S.F. Two sample subsets were
produced, the first with a target basis weight of 165 lbs/3000 ft 2
and a second with a target basis weight of 65 lbs/3000 ft 2. As
with the earlier examples, the samples produced in Example 3 also
showed an improvement in stiffness and rigidity when a crosslinker
is employed in the papermaking process. For paper products having a
target basis weight of 165 lbs/3000 ft 2, characterized in the art
as high basis weight paper, the addition of a crosslinker produced
a paper product having improved stiffness and rigidity measurements
in comparison to the control samples. Process C3, which added 60
lbs of PENFORD GUM 280 hydroxyethyl starch per ton of dry paper
pulp at the size press and 200 lbs of CURESAN 200
Glyoxal-containing crosslinker per ton of dry paper pulp at the
couch roll, showed the most improvement in stiffness and rigidity
according to the Gurley Stiffness, Ring Crush, and STFI short span
compression tests, as can be seen in Table 3.
[0078] The further addition of a polyvinyl alcohol in process C4
showed similar improvements in stiffness and rigidity, while
retaining some of the tensile and stretch properties of the control
C1 process. Additionally, higher amounts of crosslinker were found
to produce greater improvements in the stiffness and rigidity
measurements, as can be seen when comparing the results of process
C2 and C3. Similar analysis is possible from the results of the
target refining freeness of 500 ml C.S.F. with a target basis
weight of 65 lbs/3000 ft 2. For example, the results for processes
C7, C8, and C9 show that higher amounts of the crosslinker result
in more improved stiffness and rigidity measurements. These results
also show that polyvinyl alcohol may be optionally added to the
process to retain stretch, tensile, and fold properties of the
paper product.
[0079] For the tests described in Examples 1, 2, and 3, a spray
nozzle was used with the material diluted down to 3% solids by
weight to get an even spray across the web. The result was a fairly
even spray across the web. The paper machine employed for these
tests produced a 12 wide sheet. When polyvinyl alcohol was used, it
was added to the wet end at the line leading up to the headbox at
about 5% solids by weight. The polyvinyl alcohol was added as an
uncooked component in the swelled state, and was cooked in the
dryer section of the papermaking process.
[0080] It was noticed during the tests that, when the
Glyoxal-containing crosslinker was sprayed onto the wire web at the
wet end of the process, the Glyoxal-containing crosslinker caused a
much higher caliper than as expected. Without being held to the
theory, it is believed that this occurred because the
Glyoxal-containing crosslinker was acting as a bulking agent. To
adjust for this effect, some fiber was removed from the sheet. Even
with a lower fiber quantity, the test results showed an increase in
stiffness when a crosslinker was added to the process over the
control samples. Tests like, for example, M.I.T. Fold, Ring Crush
test, and STFI short span compression test, relate to the rigidity
of the paper product. As Tables 1, 2, and 3 show for the different
target basis weight and refining freeness samples, the samples
which include a crosslinker showed an increase in stiffness
measurements when compared to the control samples at the same basis
weight and freeness.
[0081] The results of the tests were more pronounced in the paper
products having lower target refining freeness. Without being held
to the theory, these lower measurements might be showing the result
of a more open sheet and thus poor retention of the material
components when being sprayed on the sheet, or otherwise added to
the process. These results may be further adjusted, and paper
products having improved rigidity and stiffness at any refining
freeness and basis weight may be produced, by changing how or where
the crosslinker is added. For example, the desired properties may
be better achieved if the same crosslinker, or different
crosslinkers, are added to the process at multiple stages, in
accordance with an embodiment of the present invention. For
example, one or more crosslinkers may be added at the size press
and/or at the wet end of the papermaking process.
Example 4
[0082] FIG. 1 shows the effect on stiffness and fold as the amount
of crosslinker is increased from 0% to 25% to 50% of the surface
sizing solution solids. As the amount of crosslinker increases, the
stiffness also increases, which fulfills the goal of achieve a
stiffened paper. The increase in the amount of crosslinker also
exhibits a detrimental effect on fold.
[0083] FIG. 2 depicts the water Cobb value when the crosslinker is
added to the process. As discussed above, water Cobb is the mass of
water in grams that absorbs into one square meter of paper in two
minutes time. The trial began with a "Control" phase 1 having no
crosslinker. The crosslinker was subsequently added with a
crosslinker feed pump, which began delivering crosslinker to the
size press. During this "Transition On" phase 2, the crosslinker
was building in concentration in the size press starch system. Data
points 3 and 4 represent "Steady State" during which the
crosslinker concentration was steadily supplied at about 60 pounds
of crosslinker per ton of paper. In phase 5, the same crosslinker
addition rate was maintained but the caliper (thickness) of the
paper was reduced. Finally, in phase 6, the crosslinker feed pump
was shut off and the crosslinker was transitioned off. The data
shows the increase in stiffness and drop in fold with increasing
concentration of crosslinker. It also shows the loss of stiffness
and recovery of fold as the crosslinker is reduced (phase 6). It
also significantly shows an increase in the water Cobb value from
control through steady state where an increasing water Cobb number
shows a loss of resistance to water. Thus, water is absorbed more
readily into the sheet when the crosslinker is added.
[0084] The examples of the present invention show that, while
polymer type materials may affect stiffness and rigidity, the
addition of a crosslinker greatly increases these properties. The
crosslinker may be added at various stages in the process such as,
for example, at the size press and/or the wet end, to produce a
paper product with improved stiffness and rigidity. The embodiments
of the present invention provide a process for making paper with
increased stiffness and rigidity, without a lamination process, and
can utilize and produce paper in a higher basis weight range since
there is no substantial addition to the total finish caliper of the
product by the present process.
[0085] Although the invention is illustrated and described herein
with reference to specific embodiments, the invention is not
intended to be limited to the details shown. Rather, various
modifications may be made in the details within the scope and range
of equivalents of the claims and without departing from the
invention.
* * * * *